1. Field of the Invention
The present invention generally concerns multiple rotating disk assemblies of the kind comprising two coaxial members of which one at least is a rotating member, a stack of disks including first disks constrained to rotate with a first of said coaxial members and second disks alternating with said first disks and constrained to rotate with the second of said coaxial members, said first and second disks being movable axially relative to said coaxial members, friction surfaces on transverse sides of at least some of said disks, and engagement means adapted to secure axial clamping of said friction surfaces between said disks.
This assembly may constitute a clutch, for example, of the type utilized on certain automotive vehicles and in particular on agricultural tractors.
One of the coaxial members is then a rotating member constrained to rotate with a first shaft, in practice a driving shaft, for example the output shaft or crankshaft of the motor of the vehicle concerned, while the other is a rotating member constrained to rotate with a second shaft, in practice a driven shaft, for example the input shaft of the associated gearbox.
When a clutch of this kind, the disks of which are usually immersed in an oil bath, is operated in order to disengage it, it is essential that the disks constrained to rotate with one of the coaxial members move sufficiently far away in the axial direction from those constrained to rotate with the other coaxial member, failing which there could arise between them an unwanted spurious driving torque, the so-called drag torque, of a kind prejudicial to the utilization of the driven shaft concerned, by virtue of the rotation to which these disks are still subject.
More specifically, this drag torque can make it difficult to engage a gear.
2. Description of the Prior Art
To minimize this drag torque by securing sufficient separation of the disks on disengagement of the clutch it has already been proposed, in particular in French Pat. No. 1 242 615, to associate with the disks constrained to rotate with one of the coaxial members, commonly referred to as intermediary disks, elastic separator members which, disposed axially between the intermediary disks, are adapted to urge them away from one another.
These may be helical coil springs, as described in French Pat. No. 1 242 615.
As an alternative, and as described in U.S. Pat. No. 3,157,257, they may comprise dished elastic annular members of the Belleville spring type, in which case they are usually retained in position by engaging them on support members carried by the associated intermediary disks. As described in U.S. Pat. No. 2,738,864, these support members may comprise tangs constituting an integral part of these intermediary disks.
Be this as it may, as is usual in the case of elastic members, the elastic limit of the elastic separator members thus used is always selected to have a sufficiently high value so as not to be exceeded in service.
In other words, it is currently commonly accepted that such elastic separator members should under no circumstances be subject to permanent deformation.
This arrangement has disadvantages, as will now be indicated.
First of all, when the friction surfaces are clamped between the disks, by virtue of actuation of the clutch engagment means, the elastic separator means associated with the intermediary disks are flattened in the axial direction and the aforementioned engagement means have to generate sufficient force in the axial direction both to overcome the oppositely directed axial force produced at this time by the elastic separator members and to provide for the transmission of a particular torque between the intermediary disks and the other disks.
The force which has to be produced in order to flatten an elastic separator member is proportional to this flattening, and this increases as the friction surfaces are progressively worn down.
Thus during the service life of the friction surfaces that part of the axial force produced by the engagement means needed for flattening the elastic separator means increases relative to that needed to transmit torque between the disks.
When the engagement means are implemented hydraulically it is possible to ensure that the axial force generated remains constant in spite of the fact that the travel progressively increases, since it is conditioned essentially by the hydraulic pressure used. This is not the case when the engagement means consist of a diaphragm spring, that is to say by the circumferentially continuous peripheral part, constituting a Belleville spring, of an annular member of which the central portion is subdivided into radial fingers to constitute clutch release levers by means of which the clutch may be actuated to disengage it.
The axial clamping force which a diaphragm spring of this kind can develop depends essentially on its initial characteristics and on the geometrical changes to which it is subject as the friction surfaces wear, due to the resulting variation in respect of the point on which it bears.
In other words, this axial force depends only on the diaphragm spring.
Thus with a diaphragm spring of this kind the part of the axial force necessary for flattening the elastic separator means increases at the expense of that available for transmitting torque between the disks.
Thus it is not possible to select the optimum diaphragm spring according only to this torque.
Moreover, as the elastic separator means may have different characteristics, the force elastically generated on releasing the clutch may also vary from one to another.
It is on this force that the moving apart of the intermediary disks concerned depends.
Thus it can happen that certain disks remain clamped when they should not, the force developed by the elastic separator members associated with the corresponding intermediary disks being less than that developed by others, and thus insufficient to balance the latter in a satisfactory manner.
A general objective of the present invention is an arrangement by means of which these disadvantages may be circumvented.